This chapter delves into superconducting qubits, starting with the essentials of superconductivity and circuit design. Central to this discussion is the Josephson junction, a key element in creating superconducting qubits. The text focuses on the transmon, the archetype in this field, while acknowledging other designs. Initialization of the transmon involves sophisticated dilution refrigerators, a process that is also examined. Additionally, the principles of circuit quantum electrodynamics (QED) are introduced as the framework for qubit control and measurement. Attention is then given to noise sources and their effect on superconducting qubits, with insights that apply to various qubit systems. The chapter wraps up by highlighting the strengths and challenges of superconducting qubits for quantum computing.

Experimental chapter that presents examples of quantum processes concerning single quantum systems, i.e. sequences comprising a state preparation part, an evolution or propagation part due to the interaction with the outer world, and a detection part. The whole sequence is repeated and its successive results stored. The examples concern quantum control of trapped ions and microwave photonsinteracting in a nondestructive way with Rydberg state cavities. It also presents "boson sampling" of photons placed in a multimode linear interferometer, a system likely to exhibit "quantum advantage," atoms trapped in an optical lattice, a promising platform for quantum simulation of complex systems, generation of "Schrödinger cats" in superconducting circuits.